This invention is generally directed to squaraine compositions, and to processes for the preparation thereof. More specifically, the present invention is directed to cyclized unsymmetrical squaraines which can be synthesized by cycloaddition-condensation processes, thereby avoiding the use of costly squaric acid as a reactant. In one ebodiment of the present invention there are provided unsymmetrical squaraine compositions containing alkylenedioxyaryl, including methylenedioxyaryl substituents with improved xerographic properties, inclusive of high charge acceptance, low dark decay, high photosensitivity, and improved cyclic stability when these compositions are incorporated into photoconductive imaging members. The squaraines can be prepared in embodiments of the present invention by cycloaddition-condensation processes thereby avoiding the use of costly squaraic acid as a reactant. Also, in an embodiment of the present invention there are provided cyclized unsymmetrical squaraines, imaging members thereof with the advantages indicated herein in embodiments of the present invention, processes for the preparation thereof, and novel squaraines. In another embodiment of the invention of the present application there are provided imaging members with photoconductive layers comprised of the unsymmetrical squaraines illustrated herein, and charge or hole transport layers, especially those comprised of aryl amines, which members are sensitive to light in the wavelength region of from about 400 to about 1,000 nanometers. The resulting members are responsive to visible light and infrared illumination originating from laser printing apparatuses wherein, for example, gallium arsenide diode lasers are selected. The photoresponsive imaging members of the present invention can also, for example, contain situated between a photogenerating layer and a hole transporting layer, or situated between a photogenerating layer and a supporting substrate with a charge transport layer in contact with the photogenerating layer, a photoconductive composition comprised of the unsymmetrical squaraines illustrated herein.
Numerous different xerographic photoconductive members, including members with photogenerating pigments of squaraines and processes thereof, are known. There are also known photoreceptor materials comprised of inorganic or organic materials wherein the charge carrier generating, and the charge carrier transport functions are accomplished by discrete contiguous layers. Additionally, layered photoreceptor materials are disclosed in the prior art, which include an overcoating layer of an electrically insulating polymeric material. Further, there are disclosed in the prior art layered photoresponsive devices including those comprised of separate generating layers, and transport layers as described in U.S. Pat. No. 4,265,990, the disclosure of which is totally incorporated herein by reference; and overcoated photoresponsive materials containing a hole injecting layer, overcoated with a hole transport layer, followed by an overcoating of a photogenerating layer; and a top coating of an insulating organic resin, reference U.S. Pat. No. 4,251,612. Examples of photogenerating layers disclosed in these patents include trigonal selenium and phthalocyanines, while examples of transport layers include certain diamines as mentioned therein. Also, there is illustrated in U.S. Pat. No. 4,415,639, the disclosure of which is totally incorporated herein by reference, the use of squaraine compositions, such as hydroxy squaraines, as a photoconductive layer in an infrared sensitive photoresponsive device. More specifically, there is described in this patent an improved photoresponsive device containing a substrate, a hole blocking layer, an optional adhesive interfacial layer, an inorganic photogenerating layer, a photoconductive composition capable of enhancing or reducing the intrinsic properties of the photogenerating layer, which photoconductive composition is selected from various squaraine compositions, including hydroxy squaraine compositions, and a hole transport layer. Other patents disclosing photoconductive devices with squaraines are U.S. Pat. Nos. 4,471,041; 4,486,520; 4,508,803; 4,507,480; 4,552,822; 4,390,610; 4,353,971; 4,391,888; 4,607,124 and 4,746,756. In the '124 patent, the disclosure of which is totally incorporated herein by reference, there are illustrated processes for the preparation of a squaraine mixture, one of which may be a fluorinated component, see column 5, wherein the known squaric acid reaction is accomplished in the presence of a fluoroaniline, and the use thereof in photoconductive imaging members. The '756 patent, the disclosure of which is totally incorporated herein by reference, illustrates layered imaging members with certain fluorinated squaraines, wherein R.sub.2 and R.sub.3 may be a heterocyclic, such as 2-pyrolyl, see columns 3, 4, 5 and 6, for example.
Furthermore, there are illustrated in U.S. Pat. No. 4,624,904, the disclosure of which is totally incorporated herein by reference, photoconductive imaging members with unsymmetrical hydroxy squaraine compositions, and aryl amine hole transport layers. The aforementioned unsymmetrical squaraine compounds can be prepared, for example, by the initial preparation of an aryl cyclobutenedione intermediate, followed by the reaction thereof with a substituted aniline. More specifically, with respect to method A illustrated in the '904 patent, the aryl cyclobutenedione is prepared by heating with reflux at a temperature of from about 40.degree. to about 50.degree. C., depending on the solvent selected; about 20 millimoles to about 50 millimoles of substituted aniline; from about 60 millimoles to about 150 millimoles of dihalocyclobutenedione; and from about 100 milliliters to about 1,000 milliliters of a Friedel-Crafts solvent inclusive of, for example, carbon disulfide nitrobenzene or methylene chloride. This reaction is accomplished in the presence of from about 200 to about 900 millimoles of a catalyst, such as aluminum chloride, and the resulting substituted aniline is reacted with a hydroxy substituted aniline in the presence of an aliphatic alcoholic solvent. Subsequent to separation, there are obtained the desired unsymmetrical squaraine compounds of the formula as detailed on page 8, beginning at line 10, for example. Also, in U.S. Pat. No. 4,521,621, there are described photoresponsive imaging members containing unsymmetrical squaraines, reference for example the formula in column 7, line 60, by forming a mixture of squaric acid, a primary alcohol, a first tertiary amine, and a second tertiary amine.
In U.S. Pat. No. 4,524,220, the disclosure of which is totally incorporated herein by reference, there is illustrated a squaraine process by the reaction of squaric acid and an aromatic aniline in the presence of an aliphatic amine. Also, in U.S. Pat. No. 4,524,219 there is described a process for the preparation of squaraines by the reaction of an alkyl squarate and an aniline in the presence of an aliphatic alcohol, and an optional acid catalyst. Moreover, disclosed in U.S. Pat. No. 4,524,218 are processes for the preparation of squaraines by the reaction of squaric acid with an aromatic amine, and a composition selected from the group consisting of phenols, and phenol squaraines, which reaction is accomplished in the presence of an aliphatic alcohol, and an optional azeotropic catalyst. Other processes for preparing squaraines are illustrated in U.S. Pat. No. 4,525,592, wherein there is described the reaction of a dialkyl squarate, and an aniline in the presence of an aliphatic alcohol and an acid catalyst; and U.S. Pat. No. 4,746,756 mentioned herein wherein the fluorinated squaraines disclosed are prepared by the reaction of an aromatic fluorinated amine and squaric acid in the presence of an aliphatic alcohol and an optional azeotropic cosolvent.
In U.S. Pat. No. 4,886,722, the disclosure of which is totally incorporated herein by reference, there is illustrated the provision of certain unsymmetrical squaraine compositions and processes for the preparation thereof. More specifically, there are disclosed in the '722 patent photoconductive imaging members containing as photoconductive compositions unsymmetrical noncyclized squaraines of the following formula ##STR2## wherein R.sub.1, R.sub.2 and R.sub.3 are independently selected from alkyl groups or aryl groups; X is hydroxy, hydrogen, alkyl, alkoxy, or halo; n is a number of from 1 to about 3; and m is a number of from 0 to about 2. Preferred halogens include fluorine and chlorine. Examples of alkyl groups include those containing from about 1 to about 25 carbon atoms such as methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, dodecyl and the like; while examples of aryl groups include those with from about 6 to about 24 carbon atoms including substituted aryl groups such as phenyl and benzyl. Alkoxy groups are represented by those containing from about 1 to about 10 carbon atoms such as methoxy, propoxy, butoxy, pentoxy, heptoxy, and the like, inclusive in some situations of aryl alkoxy substituents such as phenyl alkoxy. Halo includes fluoride, bromide, chloride and iodide.
Specific examples of unsymmetrical squaraines illustrated in the '722 patent include 4-dimethylaminophenyl-4'-methoxyphenyl squaraine; 2-hydroxy-4-dimethylaminophenyl-4'-methoxyphenyl squaraine; 2-methyl-4-dimethylaminophenyl-4'-methoxyphenyl squaraine; 2-fluoro-4-dimethylaminophenyl-4'-methoxyphenyl squaraine; 2-methoxy-4-dimethylaminophenyl-4'-methoxyphenyl squaraine; 4-benzylmethylaminophenyl-4'-methoxyphenyl squaraine; 4-dimethylaminophenyl-3',4'-dimethoxyphenyl squaraine; 2-hydroxy-4-dimethylaminophenyl-3',4'-dimethoxyphenyl squaraine; 2-methyl-4-dimethylaminophenyl-3',4'-dimethoxyphenyl squaraine; 2-fluoro-4-dimethylaminophenyl-3',4'-dimethoxyphenyl squaraine; 2-methoxy-4-dimethylaminophenyl-3',4'-dimethoxyphenyl squaraine; 4-dimethylaminophenyl-3',4',5'-trimethoxyphenyl squaraine; 2-hydroxy-4-dimethylaminophenyl-3',4',5'-trimethoxyphenyl squaraine; 2-chloro-4-dimethylaminophenyl-4'-methoxyphenyl squaraine; 2-chloro-4-dimethylaminophenyl-3',4'-dimethoxyphenyl squaraine; 4-diethylaminophenyl-4'-methoxyphenyl squaraine; and 4-diethylaminophenyl-3',4'-dimethoxyphenyl squaraine.
The squaraine compositions of the '722 patent are generally prepared by a cycloaddition-condensation reaction. More specifically, these squaraines can be prepared by condensing, for example, a 1-alkoxyaryl-2-hydroxycyclobutene-3,4-dione derivative with an N,N-dialkylaniline derivative, such as 1-3',4'-dimethoxyphenyl-2-hydroxycyclobutene-3,4-dione or 3-fluoro-N,N-dimethylaniline in a molar ratio of about 1 to 6, and preferably in a ratio of about 1 to 3 in the presence of an aliphatic alcohol, such as propanol, and an optional drying reagent. About 500 milliliters of alcohol per 0.1 mole of 1-alkoxyaryl-2-hydroxycyclobutene-3,4-dione are selected, however, up to about 1,000 milliliters of alcohol to about 0.5 to 1 mole of 1-alkoxyaryl-2-hydroxycyclobutene-3,4-dione can be selected. The drying reagent can be heterogeneous, such as molecular sieves, or homogeneous, such as a trialkyl orthoformate. A ratio of 1 to 10 equivalents of drying reagent, more specifically tributyl orthoformate, can be used with a ratio of about 1 to 4 to the cyclobutene dione being preferred. Also, the reaction is generally accomplished at a temperature of about 60.degree. C. to about 130.degree. C., and preferably at a temperature of 70.degree. C. to about 100.degree. C. with stirring until the reaction is completed. Subsequently, the desired product can be isolated from the reaction mixture by known techniques such as filtration, and the product is identified by analytical tools including IR, NMR, and mass spectrometry. Further, carbon, hydrogen, fluorine, nitrogen and oxygen elemental analysis can be selected for aiding the identification of the product.
The 1-alkoxyaryl-2-hydroxycyclobutene-3,4-dione reactant can be prepared as indicated in the literature, and specifically by a known [2+2] cycloaddition process involving a tetraalkoxy olefin and an alkoxyarylketene generated in situ by the reaction of an alkoxyarylacetyl chloride and a base. Thus, for example, 3,4-dimethoxyphenylacetyl chloride can be reacted with tetraethoxyethylene in n-hexane in the presence of triethylamine. The ratio of acid chloride to tetraethoxyethylene is about 1 to 10 with 1 to 4 being preferred. The amount of triethylamine used will vary, however, usually an amount equivalent to the amount of the acid chloride is selected, and the reaction mixture is stirred at room temperature until the reaction is complete. Also, the [2+2] cyclo adduct product mixture can be hydrolyzed directly by refluxing in an aqueous hydrochloric acid solution or pre-purified by stirring with silica gel or alumina in a solvent, such as n-hexane or ether, before the hydrolysis. The hydrolyzed product is then purified by conventional technique such as recrystallization. This results in reactants such as 1-4'-methoxyphenyl-2-hydroxycyclobutene-3,4-dione, 1-3',4'-dimethoxyphenyl-2-hydroxycyclobutene-3,4-dione, and 1-3',4',5' -trimethoxyphenyl-2-hydroxycyclobutene-3,4-dione, which can then be reacted with a N,N-dialkylaniline enabling the formation of the unsymmetrical squaraines.
The squaraines of the aforementioned '722 patent can be incorporated into various photoconductive imaging members. One such member is comprised of a supporting substrate, a hole transport layer and as a photoconductive layer situated between the supporting substrate, and the hole transport layer the squaraines. In another embodiment of the copending application, there is envisioned a layered photoresponsive device comprised of a supporting substrate, a certain squaraine photoconductive layer and situated between the supporting substrate and the photoconductive layer, a hole transport layer. In one specific illustrative embodiment of the copending application, the photoresponsive device can be comprised of (1) a supporting substrate, (2) a hole blocking layer, (3) an optional adhesive interface layer, (4) an unsymmetrical squaraine photogenerating layer, and (5) a hole transport layer. Thus, a specific photoresponsive device of the copending application can be comprised of a conductive supporting substrate, a hole blocking metal oxide layer in contact therewith, an adhesive layer, an unsymmetrical squaraine photogenerating material overcoated on the optional adhesive layer, and as a top layer, a hole transport layer comprised of certain diamines dispersed in a resinous matrix. The photoconductive layer composition, when in contact with the hole transport layer, is capable of allowing holes generated by the photogenerating layer to be transported. Examples of aryl amine hole transport molecules that may be selected for the photoconductor devices are illustrated in U.S. Pat. No. 4,265,990, the disclosure of which is totally incorporated herein by reference.
The photoresponsive devices described in the '722 patent and the imaging members of the present invention can be utilized in various imaging systems including xerographic imaging processes. Additionally, the imaging members of the present invention can be selected for imaging and printing systems with visible light and/or infrared light. In this embodiment, the photoresponsive devices may be negatively charged, exposed to light in a wavelength of from about 400 to about 850 nanometers, either sequentially or simultaneously, followed by developing the resulting image and transferring to paper. The above sequence may be repeated many times.
The following prior art is also mentioned: U.S. Pat. Nos. 4,521,621; 4,607,124 and 4,746,756, mentioned hereinbefore, of which the '756 patent illustrates fluorinated squaraines wherein R.sub.1, R.sub.2 and R.sub.3 may be a heterocyclic, see column 5, lines 4 to 29, for example. Further, in Angew Chem. Int. Ed. Engl 5, 894 (1966), H. E. Spenger and W. Ziegenbein there is illustrated the preparation of squaraines by condensing one equivalent of squaric acid and two equivalents of aniline derivatives under azeotropic conditions; many squaraines have been prepared by the aforementioned processes, reference for example U.S. Pat. Nos. 3,617,270; 3,824,099; 4,175,956; 4,486,520 and 4,508,803; and hydroxy and certain fluorinated squaraines for xerographic photoreceptor applications, reference K. Y. Law and F. C. Bailey, J. Imaging Science, 31, 172 (1987).
In copending application U.S. Ser. No. 524,947, the disclosure of which is totally incorporated herein by reference, there are illustrated photoconductive imaging members with photoconductive fluorinated squaraine compositions of the formulas indicated including bis(2-fluoro-4-N-pyrrolidinophenyl) squaraine; 2-fluoro-4-N-pyrrolidinophenyl-4'-dimethylaminophenyl squaraine; 2-fluoro-4-N-pyrrolidinophenyl-2'-hydroxy-4'-dimethylaminophenyl squaraine; 2-fluoro-4-N-pyrrolidinophenyl-2'-methyl-4'-dimethylaminophenyl squaraine; 2-fluoro-4-N-pyrrolidinophenyl-4'-dimethylaminophenyl squaraine; 2-fluoro-4-N-pyrrolidinophenyl-4'-methoxyphenyl squaraine; 2-fluoro-4-N-pyrrolidinophenyl-3',4'-dimethoxyphenyl squaraine; 2-fluoro-4-N-pyrrolidinophenyl-3',4',5'-trimethoxyphenyl squaraine; 2-fluoro-4-N-pyrrolidinophenyl-2'-methoxy-4'-dimethylaminophenyl squaraine; 2-fluoro-4-N-pyrrolidinophenyl-4'-methylbenzylaminophenyl squaraine; 2-fluoro-4-N-pyrrolidinophenyl-2'-chloro-4'-dimethylaminophenyl squaraine; 2-fluoro-4-N-pyrrolidinophenyl-9'-julolidinyl squaraine; 2-fluoro-4-N-pyrrolidinophenyl-8'-hydroxy-9'-julolidinyl squaraine; and 2-fluoro-4-N-pyrrolidinophenyl-8'-fluoro-9'-julolidinyl squaraine.
Although the above squaraines and processes thereof are suitable for their intended purposes, there continues to be a need for other photoconductive squaraines. Additionally, and more specifically there remains a need for simple, economical processes for preparing certain squaraine compositions with stable properties, which when incorporated into photoconductive devices can result in reduced dark decay characteristics, and increased charge acceptance values as compared to many similar squaraine compositions. In addition, there remains a need for photoconductive imaging members with certain stable electrical characteristics, that is for example the aforementioned imaging members are electrically stable for over 50,000 xerographic imaging cycles in embodiments thereof. In addition, imaging members with the squaraines of the present invention in embodiments thereof are sensitive to a broad range of wavelengths, including visible and infrared light, such as of from about 400 to about 850 nanometers, enabling such members to be useful in electrophotographic imaging and printing processes, including processes wherein diode lasers, or LED (light emitted diodes) image bars are selected.